Method for strenghtnening a metal surface

ABSTRACT

A metal surface strengthening method comprising attaching, with or without pressure, a preformed plate formed of a metal surface strengthening powder to a fundamental molten metal kept in a gas sprayed protective atmosphere in the mold.

waited States Patent [191 Sakai et a1.

[ Feb. 19, 1974 METHOD FOR STRENGHTNENING A METAL SURFACE [75]Inventors: Yoshifumi Sakai, Chiryu; Takeshi Sumi, Chita; Atsushi Wada,Tokai; Mitsuo Morishima, Tokai; Shigeto Kawakaki, Tokai; Takashi Kozawa,Nagoya, all of Japan [73] Assignee: Daido Deiko Kabushiki Kaisha,

' Aichi-ken, Japan [22] Filed: Dec. 22, 1971 21 App1. No.5 210,733

[30] Foreign Application Priority Data Dec. 29, 1970 Japan 45/121220[52] 11.5}. C1 164/59, 164/98, 164/120 [51] Int. Cl B22d 19/00, 322d27/18 [58] Field of Search. 164/59, 75, 120, 98, 100, 103,

[56] References Cited UNITED STATES PATENTS 2,161,597 6/1939 Swartz164/75 X 2,034,550 3/1936 Adams 164/98 X FOREIGN PATENTS OR APPLICATIONS431,372 1/1968 Japan 164/97 Primary ExaminerJ. Spencer OverholserAssistant Examiner-John E. Roethel 5 7 ABSTRACT A metal surfacestrengthening method comprising attaching, with or without pressure, apreformed plate formed of a metal surface strengthening powder to afundamental molten metal kept in a gas sprayed protective atmosphere inthe mold.

2 Claims, 7 Drawing Figures PATENTEB FEB l 9 I974 SHEET 1 [IF 2 FIG.4

FIG.

FIG.5

FIG.6

PATENTED 3.792.726

sum 2 OF 2 VICKERS HARDNESS (HV) VALUES IN EACH LEVEL OF MICROSTRUCTUREFIG.7

METHOD F OR STRENGHTNENING A METAL SURFACE BACKGROUND OF THE INVENTIONing is under development (e.g., Japanese Pat. No. I

520,699). This method is concerned with an applied technique of squeezecasting, wherein the metal surface strengthening powder is directlyscattered on wherein molten metal poured in the mold, and the pressureis subsequently applied thereto to form a strengthened metal layer. Thismethod enables one to obtain the desired strengthened metal layersimultaneously with the completion of the product, and so is a method tobe highly appreciated. At present, however, this method has drawbacks asmentioned below:

1. Since the molten metal surface in the mold is in an oxidized state atthe time the powder is scattered thereon, the reaction between thepowder and the molten metal becomes incomplete so that even if thepressure is sufficiently applied thereto, the resulting product oftentends to tear off at the bonded portion.

2. Furthermore, as the powder, when scattered on the molten surface, isheated by the molten metal and is oxidized by oxygen in the air, it maylose its metal strengthening nature. For example, if the powder is of WC(tungsten carbide), W in the WC reacts with O so that the resultinglayer is not sufficiently strengthened.

Because of these disadvantages, it has been difficult, as shown in FIGS.1 and 2, to form products with smooth casting surfaces and uniformstrengthened layers (A).

SUMMARY OF INVENTION This invention relates to a method forstrengthening a metal surface comprising the steps of pouring a moltenmetal into a mold, placing or laying a preformed plate compacted from amixture of one ormore of a powder of tungsten carbide, titanium carbide,tantalum carbide and ceramic and a powder of a binder on the surface ofsaid molten metal, and applying pressure by means of a punch during themolten state or solidification course of said molten metal so that saidplate is directly bonded to the surface of said metal whereby astrengthening layer is formed on the surface of said metal.

This invention aims at removing the defects mentioned hereinbefore,permitting strengthening of the metal surface by a relatively simplemethod, and further, permitting industrial mass production for themethod.

BRIEF DESCRIPTION OF THE DRAWINGS metal layer strengthened in accordancewith the con ventional powder scattering method;

FIG. 3 is a cross sectional view of one embodiment of this invention;and

FIGS. 4 7 are photomicrographs and a diagram of the embodiments effectedin accordance with the present invention, wherein FIG. 4 is aphotomicrograph (X of the casting surface of a strengthened layer; FIG.5 is a photomicrograph (X k) of a. section of the thickness distributionof a strengthened layer; FIG. 6 is a photomicrograph (X 100) of themicrostructure of the bonded part of a strengthened layer with afundamental material; and FIG. 7 is a diagram of the distribution ofhardness (Hv) of the strengthened layer shown in FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENTS The method of this invention willnow be explained with reference to FIG. 3 of the accompanying drawings.I

The preformed plate is formed to one '5 mm thick piece from a mixture laof the powder comprising at least percent of one or more of tungstencarbide, titanium carbide, tantalum carbide, ceramics, etc., each havinga good affinity with the molten metal, and approximately 10 percent of abinder such as a thermosetting resin, on an asbestine adiabatic sheet I1b producting no slag when reacted with the molten metal.

A desired molten metal 3 is then poured into the mold 2 which is sprayedwith a wash for accomplishing a releasing action at the inside wall ofsaid mold, when the atmosphere in the mold 2 is kept non-oxidizedprotective to prevent the molten metal 3 from oxidizing. For thispurpose, the nozzles 7 provided at the upper inside of the mold 2 areconnected to the protective gas supplying pipe 6. The preformed plate 1is then placed or laid on the surface of the molten metal 3, and after alapse ofa proper time (e.g., about 10 sec.) a pressure punch 4 islowered to apply thereto an amount of pressure (e.g., about 1 tonlcmabout 30 sec.). Thereafter, the pressure is released and the product ofa predetermined shape is taken out by means of a knockout pin 5.

FIG. 4 shows a casting surface of a strengthened surface formedaccording to the method of this invention and FIG. 5 illustrates astrengthened layer (B) formed by the method of this invention. It hasbeen found that both of them have the merits as mentioned hereinafter incomparison with the conventional scattering method. As is clear from thecomparison of FIG. 1 with FIG. 4, the casting surface is superior in thecase of the present invention. For instance, the shortcomings such asblow holes, tearing off of the strengthened layer,

etc., that have often taken place with the prior method have beenremarkably decreased. A comparison of the reference numeral A of FIG. 2with the reference numeral B of FIG. 5 clearly shows that thestrengthened layer with a uniform and desired thickness as shown in FIG.5 can also be obtained by the method of the present invention.

Furthermore, in the product obtained by the method of this invention,the strengthened layer is so firmly bonded to the molten metal due tothe application of pressure by means of the punch 4 that, when used fora punching die and the like requiring a substantial hardness and atoughness, such undesirable phenomena as half-wearing, lacking, andtearing-off in the case of the conventional die do not occur so that aremarkable effect results in that the life span of the product isprolonged.

FIG. 6 represents the microstructure (X 100) of the bonded part of thestrengthened layer to the fundamental material obtained by the method ofthe present invention. This test material has been prepared by bondingto the molten metal of carbon steel a preformed plate formed of WC(tungsten carbide) powder, said test material having been subjected toan annealing process thereafter. From this figure, it can be seen thatthe attachment near the boundary portion (C) is perfect and no noxiousdefects such as an inclusion or gas effect are recognized.

FIG. 7 is a diagram showing the distribution of Vickers hardness (I-Iv)extending from the strengthened layer as shown in the photomic'rographof FIG. 6 to the fundamental material. As is clear from the diagram, thestrengthened layer (made from tungsten carbide) re- I mains sufficientlystrengthened after it has been annealed.

As described above in detail, it has been shown that the method of thepresent invention is far superior to that of the conventional powderscattering method. For instance, in case a strengthened layer is to beattached to an uneven metal surface, it has been very difficult toattach it uniformly due to the fluidity of the molten metal. Accordingto this invention, however, a pre formed plate formed to any desiredshape from the powder for strengthening a metal surfaceis placed or laidon the molten metal in the mold or core mold so that products withevenly strengthened surfaces can be obtained.

According to the present invention, as described above, the metalsurface strengthening can be carried out by the relatively simplemethod. Moreover, various composite materials in the fields of wearing,heat, and erosion resistance industries can be manufactured atremarkably low costs. Also, the object of using the preformed plate inthis invention is that the operation can be carried out effectively anda smoothed casting surface and uniform thickness of strengthened layercan be obtained. Furthermore, in case the features of the molten metaland those of the powder for strenghening are quite different therebymaking the attachment therebetween difficult, they can be attached byadding to the preformed plate one or more layers of materials requiredfor their attachment.

What is claimed is:

1. A method for strengthening a metal surface comprising the steps ofpouring a molten metal into a mold, placing a preformed plate compactedfrom a mixture of one or more of a powder of tungsten carbide, titaniumcarbide, tantalum carbide and ceramics and a powder of a binder on thesurface of said molten metal, and applying pressure by means of a punchduring the molten state of said molten metal so that said plate isdirectly bonded to the surface of said metal whereby a strengthenedlayer is formed on the surface of said metal.

2. The method of claim 1 wherein the pressure is applied during thesolidification of said molten metal.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,792,726 DatedFebruary 19, 197

Patent No.

Inventor) Yoshifumi Sakai, Takeshi Sumi, et al It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the first page, column 1, line 8, the Assignee's name should read--Daido Seikoinstead of "Daido Deiko" Signed and sealed this 13th day ofAugust 197 (SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN I =Attesting Officer Commissionerof Patents ORM po'mso USCOMM-DC wan-ps9 U. 5. GOVERNMENT PRINTlNG OFFICEt '9', U3 33,

1. A method for strengthening a metal surface comprising the steps ofpouring a molten metal into a mold, placing a preformed plate compactedfrom a mixture of one or more of a powder of tungsten carbide, titaniumcarbide, tantalum carbide and ceramics and a powder of a binder on thesurface of said molten metal, and applying pressure by means of a punchduring the molten state of said molten metal so that said plate isdirectly bonded to the surface of said metal whereby a strengthenedlayer is formed on the surface of said metal.
 2. The method of claim 1wherein the pressure is applied during the solidification of said moltenmetal.